Docetaxel (Taxotere) is a new chemotherapeutic agent which has shown promise in the treatment of various malignancies including cancers of the breast, lung, ovary, stomach, head and neck, bladder, and soft tissue sarcomas. Docetaxel undergoes metabolism by cytochrome P450 3A in human liver microsomes. Patients treated with the same dose of docetaxel per body surface area exhibit interpatient variation in clearance and degree of toxicity. We hypothesize that cytochrome P450 3A is rate limiting in the elimination of docetaxel and that changes in P450 3A activity will result in interpatient and intrapatient variation in docetaxel's clearance.